As the dielectric constant of the substrate increases, the antenna bandwidth decreases which increases the Q factor of the antenna and therefore decreases the impedance bandwidth. The dielectric loading of a microstrip antenna affects both its radiation pattern and impedance bandwidth. An early model of the microstrip antenna is a section of microstrip transmission line with equivalent loads on either end to represent the radiation loss. The resonant length of the antenna is slightly shorter because of the extended electric fringing fields which increase the electrical length of the antenna slightly. As the antenna is loaded with a dielectric as its substrate, the length of the antenna decreases as the relative dielectric constant of the substrate increases. When air is used as the dielectric substrate, the length of the rectangular microstrip antenna is approximately one-half of a free-space wavelength. It is approximately of one-half wavelength long.
The most commonly employed microstrip antenna is a rectangular patch which looks like a truncated microstrip transmission line. 2 This unique property allows patch antennas to be used in many types of communications links that may have varied requirements. Patch antennas can easily be designed to have vertical, horizontal, right hand circular RHCP or left hand circular LHCP polarizations, using multiple feed points, or a single feedpoint with asymmetric patch structures. 1Īn advantage inherent to patch antennas is the ability to have polarization diversity. Such an array of patch antennas is an easy way to make a phased array of antennas with dynamic beamforming ability. The ability to create high gain arrays in a low-profile antenna is one reason that patch arrays are common on airplanes and in other military applications. Patch arrays can provide much higher gains than a single patch at little additional cost matching and phase adjustment can be performed with printed microstrip feed structures, again in the same operations that form the radiating patches. It is relatively easy to print an array of patches on a single large substrate using lithographic techniques. A single patch antenna provides a maximum directive gain of around 6-9 dBi. They are usually employed at UHF and higher frequencies because the size of the antenna is directly tied to the wavelength at the resonant frequency. Microstrip antennas are relatively inexpensive to manufacture and design because of the simple 2-dimensional physical geometry.
Because such antennas have a very low profile, are mechanically rugged and can be shaped to conform to the curving skin of a vehicle, they are often mounted on the exterior of aircraft and spacecraft, or are incorporated into mobile radio communications devices. Some patch antennas do not use a dielectric substrate and instead are made of a metal patch mounted above a ground plane using dielectric spacers the resulting structure is less rugged but has a wider bandwidth. Common microstrip antenna shapes are square, rectangular, circular and elliptical, but any continuous shape is possible. In telecommunication, there are several types of microstrip antennas also known as printed antennas the most common of which is the microstrip patch antenna or patch antenna.Ī patch antenna is a narrowband, wide-beam antenna fabricated by etching the antenna element pattern in metal trace bonded to an insulating dielectric substrate, such as a printed circuit board, with a continuous metal layer bonded to the opposite side of the substrate which forms a ground plane. The conductance due to the radiated power of the circular microstrip patch antenna can be computed based on the the radiated power expressed as Balanis, 1982.